The invention relates to cement dispersing agents for self-compacting concrete of high flowability. When an aqueous solution of the inventive dispersing agent is used as an admixture to freshly prepared concrete of extremely low water-to-cement ratio, a high fluidity, a low decrease in flowability with the progression of time and an absence of segregation over time is achieved.
Concrete from ready mix plants or mixed on job sites, used in civil engineering constructions, e.g. anchorage of big bridges, base plates or side walls and box culverts, in building structures such as heavy reinforced structures, concrete filling pipe structures or other complicated structures, demands to be fully compacted to achieve its required strength and durability. The existing and conventional method for compacting is by vibration of the freshly placed concrete.
A new production system for in situ-casted concrete is needed to improve significantly the cost situation as well as the health and safety aspects on the construction site.
Additionally, self compacting concrete leads to a higher productivity, shorter building times and to an improved labour environment.
Increased fluidity (known as "slump" and slump-flow) can be realized by using large dosages of water in the concrete, but it is well known that the resulting cement-based structure exhibits insufficient compactness and will have poor final compressive strength.
In order to avoid excess amount of water, flowing concrete can be produced by the addition of so-called superplasticizers or high range water-reducing admixtures (HRWRs) like sulphonated melamine- or naphthalene-formaldehyde polycondensates or ligninsulphonate based admixtures. All of these well known materials are not capable of causing the treated cement compositions to retain high flowability over a sustained period of time (known as "slump life") without imparting a significant delay in the initial set time and considerable retardation of early strengths.
More recently, various additives based on so called polycarboxylic acid salts, e.g. copolymers of acrylic acid with acrylic esters have been proposed for imparting high water reduction and prolonged slump life to concrete, but most of them do not lead to self-compacting concrete without bleeding, segregation or cause a too long retardation of the setting time and the strength development. An additional disadvantage is the inconstant and very low flow rate of high-flowing--high-strength concrete, containing high quantities (e.g. 500 to 700 kgs/m.sup.3) of cement and up to 20% of silica fume and fly ash, which flow rate cannot be improved by the use of conventional HRWRs.